A、To establish his laboratory. B、To have a vacation. C、To visit members of his family. D、To study deafness among the families. D

Good morning students. This class I brought two books that I had been reading. I want to introduce them to you because I hope you have been able m read the two hooks. They are about speech and hearing problems that I put in the library. (26) Today’s lecture deals with the presence of the unusually large deaf population that had existed on the Massachusetts island of Martha’s Vineyard for about three centuries. From the settlement of the island in the 1640s to the 20th century, the people there, who were descended from only twenty-five or thirty original families, married mainly other residents of the island. They formed a highly inbred group, producing an excellent example of the genetic patterns for the inheritance of deafness. Indeed in the lair: 1800s, one out of every twenty-five people in one village on the island was born deaf and the island as a whole had a deafness rate at least seventeen times greater than that of the rest of the United Status. (27) Even Alexander Graham Bell, the inventor of the telephone and a prominent researcher into hearing loss, visited Martha’s Vineyard to study the population. But because the principles of genetics and inheritance were still unknown, he was not able to explain the patterns of deafness and why a deaf parent did not always have deaf children. (28) In the 20th century, the local population has mixed with people off the island and the rate of deafness has fallen.